Currently, smart wearable devices, especially smart watches, have developed rapidly. For the smart watch with a circular or near-circular dial, it is necessary to provide a circular or near-circular backlight source, especially a circular or near-circular light guide plate in the backlight source.
For example, for the design of the circular or near-circular light guide plate, essentially a direct-type or edge-type backlight source structure is adopted. Of course, during the design of the light guide plate having any other shapes, the direct-type or edge-type backlight source structure may also be adopted in accordance with the practical need.
In the case of the direct-type backlight source structure, the light guide plate needs to occupy a large space, so it is impossible to meet the requirements on the mass production of small-size and super-thin products. In the case of the edge-type backlight source structure, light-emitting diodes (LEDs), serving as the backlight source, each has a flat light-emitting surface, while a lateral surface of the circular light guide plate is round. Hence, light loss may easily occur for the LED light source due to the circular light guide plate, and it is difficult to assemble the light guide plate with the backlight source.